1. Field of the Invention
The present invention relates to a method for wireless data transmission between a base station and a transponder, whereby a message, comprising at least one command and one data sequence, is transmitted by the base station and the message is received and evaluated by the transponder. The invention relates further to a transponder and to a system for rapid data transmission.
2. Description of the Background Art
Methods for wireless data transmission are used, for example, in contactless identification systems or so-called Radio Frequency Identification (RFID) systems. This type of system typically includes a base station or a reader or a reader unit and a plurality of transponders or remote sensors, which are located simultaneously within the response range of the base station. The transponders or their transmitting and receiving devices typically do not have an active transmitter for data transmission to the base station. Such inactive systems are called passive systems when they do not have their own power supply and semipassive systems when they have their own power supply. Passive transponders draw the power necessary for their supply from the electromagnetic field emitted by the base station.
Backscatter coupling is employed, as a rule, for data transmission from a transponder to a base station with UHF or microwaves in the far field of the base station. To that end, the base station emits electromagnetic carrier waves, which are modulated and reflected by the transmitting and receiving device of the transponder by means of a modulation method in accordance with the data to be transmitted to the base station. The typical modulation methods for this are amplitude modulation, phase modulation, and amplitude shift keying (ASK) subcarrier modulation, in which the frequency or the phase position of the subcarrier is modified.
In a data transmission between a base station and a transponder, for reasons of security and/or data protection, third parties must be prevented from being able to intercept the transmitted data. The transponder transmits the data to the base station at a low RF level. Interception is therefore possible only with increased effort. The base station, in contrast, usually transmits at a high RF level, so that interception of the transmitted data is also possible at great distances.
In order to increase data transmission security, it is generally known to encrypt the transmitted data by cryptographic methods. These cryptographic methods are usually based on random numbers, which must be exchanged between the transponder and base station. Thus, for example, the draft standard ISO/IEC_CD 18000-SC of 7 Jan. 2005 provides that write access by a base station to a transponder is preceded by a request for a random number. Based on the request, the transponder transmits a random number to the base station, which the base station uses to encrypt the data for the subsequent write access. For transmission of an access password, a block command, or for other transmissions as well, before transmission of data, random numbers for their encryption are to be exchanged.
An exchange of this kind at the front end is associated with a high time expenditure.